CCing the list back. At Fri, 28 Sep 2012 13:30:52 -0700, Alexander Solla wrote:
What is the problem, exactly? It looks to me like UndecidableInstances and ScopedTypeVariables (on foo, or its arguments) would be enough.
I'm not sure what you mean. I don't see the need for UndecidableInstances, and there is no way I can see to bring the `b' into scope in the type sig for foo, ScopedTypeVariables or not - unless I'm missing something.
Also note that as stated, foo's type "is a bottom" (more specifically, is a function onto bottom, since c is free in the class, and so foo must be parametrically polymorphic in its return type, and so is devoid of "real" Haskell values). Hopefully that is just an artefact of the translation to Foo's and Bar's.
Yeah the type for `foo' is irrelevant, I just needed to put something there. -- Francesco * Often in error, never in doubt